WHAT’S THE DIFFERENCE BETWEEN WEIGHT LOSS AND FAT LOSS?

Men's Fitness consulted Dr. Joel Seedman for this article, which originally appeared at mensfitness.com.

Losing lbs isn’t always a good thing—here's how to know if your efforts in the gym and kitchen are actually paying off.

Ditching the layer of fat covering your six pack means you’re cutting calories and increasing your burn. But seeing the scale flash three pounds less than last week doesn’t necessarily mean all your hardwork is paying off.

There’s three explanations for weight loss, says strength and performance specialist Joel Seedman, Ph.D., owner of Advanced Human Performance (Atlanta, GA): Losing fat, losing muscle, and losing water. With a perfect diet and workout regimen, you’ll just be shedding fat. But because there are so many moving parts when it comes to dieting and working out, chances may also be losing weight you’d rather keep.

1. Muscle Loss

Muscle requires constant work to maintain—we all know this. But if your attention is on fixing your diet or upping your cardio in order to burn fat, that focus is probably coming at the expense of strength training.

Plus, if you’re more focused on your calorie restriction than working out, you’ll almost assuredly lose muscle tissue weight, Seedman says. Why? Because calorie restriction usually means macronutrient restriction. Without enough protein in your diet, your body can’t rebuild the tissue even if you are strength training.

Not only is it a bummer to forfeit those gains, but muscle directly impacts your basal metabolic rate (BMR)—or the rate at which your body burns calories both while working out as well as at rest. Less muscle means a lower BMR which means a lower calorie burn throughout your day.

Muscle tissue also regulates your insulin sensitivity—the biological process that determines how well your body absorbs nutrients. If you lose muscle tissue from dieting improperly, the nutrients you eat are less likely to be partitioned to your muscle cells and more likely to be turned into fat cells, Seedman adds.

2. Water Loss

One of the fastest ways to lose weight in the short-term is to cut carbs—that’s because carbohydrates retain some three times as much water as any other type of macronutrient, Seedman explains. When you cut back on carbs, your body isn’t retaining as much water, plain and simple.

But losing water weight is like buffing your car—it makes the exterior look sleeker, but the beautification is short lived and no interior improvements have actually been made. “If you lose intermuscular water, at first it’s not a big deal—it’s like letting a little air out of a balloon,” Seedman explains. But after a few weeks, because muscle is 70 percent water, the tissue adapts to the dehydration and your muscles shrink and start to atrophy. You’re not only compromising the structural integrity of your muscles, but as you lose bulk thanks to the lack of water, you’re also triggering the whole metabolic dysfunction of BMR and insulin sensitivity that comes with losing muscle.

The problem comes when you drop below 50 to 75 grams of carbs on a consistent basis, Seedman adds. You still need to eat some carbs—at least .5 grams per pound of your body weight for a low-carb diet or .75 to 1.5 grams per pound for a more balanced calorie-restricted diet will allow fat loss without losing that intramuscular water.

3. Fat Loss

Your aim is for maximum lipolysisis—the biological process of breaking down fat lipids and triglycerides in either the food you eat or that are already stored in your body. This mostly happens in the mitochondria of the muscles, which is why the more muscle you have, the more fat you burn, Seedman points out. Exercise has also been shown to upregulate those lipolytic enzymes and improve mitochondria function, which is why working out helps you shed fat.

While that sounds pretty straightforward, it’s actually incredibly hard to predict your potential burn rate. “It’s not just calories in, calories out,” Seedman clarifies. While traditional thinking was that between your BMR and calorie intake, you could calculate how much fat you’ll lose per week. But there are an infinite number of possibilities that can occur among the different enzymes, hormonal response, biochemical reactions, and endocrine function—just to name a few—which can all affect this rate, he adds.

4. How Do You Know?

If you see more than two pounds disappear in a week, you’re dealing with more than just fat loss. “When guys start upping their workouts and cutting calories, they’ll see fat loss pretty quickly—but never at a rapid rate,” Seedman explains. This two-pounds-a-week is most everybody's threshold for fat burn. If you drop 10 pounds in a week, the vast majority of that will be water weight and a little bit of muscle loss as well.